minitest provides a complete suite of testing facilities supporting
TDD, BDD, mocking, and benchmarking.
"I had a class with Jim Weirich on testing last week and we were
allowed to choose our testing frameworks. Kirk Haines and I were
paired up and we cracked open the code for a few test
frameworks...
I MUST say that minitest is *very* readable / understandable
compared to the 'other two' options we looked at. Nicely done and
thank you for helping us keep our mental sanity."
-- Wayne E. Seguin
minitest/unit is a small and incredibly fast unit testing framework.
It provides a rich set of assertions to make your tests clean and
readable.
minitest/spec is a functionally complete spec engine. It hooks onto
minitest/unit and seamlessly bridges test assertions over to spec
expectations.
minitest/benchmark is an awesome way to assert the performance of your
algorithms in a repeatable manner. Now you can assert that your newb
co-worker doesn't replace your linear algorithm with an exponential
one!
minitest/mock by Steven Baker, is a beautifully tiny mock (and stub)
object framework.
minitest/pride shows pride in testing and adds coloring to your test
output. I guess it is an example of how to write IO pipes too. :P
minitest/unit is meant to have a clean implementation for language
implementors that need a minimal set of methods to bootstrap a working
test suite. For example, there is no magic involved for test-case
discovery.
"Again, I can't praise enough the idea of a testing/specing
framework that I can actually read in full in one sitting!"
-- Piotr Szotkowski
Comparing to rspec:
rspec is a testing DSL. minitest is ruby.
-- Adam Hawkins, "Bow Before MiniTest"
minitest doesn't reinvent anything that ruby already provides, like:
classes, modules, inheritance, methods. This means you only have to
learn ruby to use minitest and all of your regular OO practices like
extract-method refactorings still apply.

Rake is a Make-like program implemented in Ruby. Tasks and dependencies are
specified in standard Ruby syntax.
Rake has the following features:
* Rakefiles (rake's version of Makefiles) are completely defined in
standard Ruby syntax. No XML files to edit. No quirky Makefile
syntax to worry about (is that a tab or a space?)
* Users can specify tasks with prerequisites.
* Rake supports rule patterns to synthesize implicit tasks.
* Flexible FileLists that act like arrays but know about manipulating
file names and paths.
* A library of prepackaged tasks to make building rakefiles easier. For example,
tasks for building tarballs and publishing to FTP or SSH sites. (Formerly
tasks for building RDoc and Gems were included in rake but they're now
available in RDoc and RubyGems respectively.)
* Supports parallel execution of tasks.

YARD is a documentation generation tool for the Ruby programming language.
It enables the user to generate consistent, usable documentation that can be
exported to a number of formats very easily, and also supports extending for
custom Ruby constructs such as custom class level definitions.